Pressure mold for removing liquid from material being cast

ABSTRACT

Grooved plates and end grain redwood boards are combined to form a filtering means used in the preparation of high strength cementitious material.

United States Patent 1191 Wilson et al.

FROM MATERIAL BEING CAST [75] Inventors: John E. Wilson, Salt Lake City,Utah; Carl F. Austin, lnyokem, Calif.; William H. Sayler, Salt LakeCity, Utah [73] Assignee: The United States of America as represented bythe Secretary of the Navy, Washington, DC. by said Austin [22] Filed:May 25, 1972 [21] Appl. No.: 256,831

[52] US. Cl 425/84, 425/420, 425/812,

425/D1G. 119, 425/D1G. 119, 100/116, 100/126 [51] Int. Cl .Q 1328b 3/04[58] Field of Search 425/84, 85, 420,

425/812, DIG. 119; 100/116, 126; 106/89 PRESSURE MOLD FOR REMOVINGLIQUID v 1111 3,756,756 1 1 Sept. 4, 1973 Primary Examiner- R. SpencerAnnear A norney- R. S. Sciascia, Roy Miller et al.

ABSTRACT Grooved plates and end grain redwood boards are combined toform a filtering means used in the preparation of high strengthcementitious material.

1 Claim, 4 Drawing Figures PATENTED SEP 41973 FIG.

FIG. I.

FIG.

FIG. 3.

PRESSURE MOLD FOR REMOVING LIQUID FROM MATERIAL BEING CAST BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates toapparatus and a method for preparing high strength cementitiousmaterial. More particularly, this invention relates to apparatus and amethod for removing excess water and air from freshly mixed cementitiousmaterial prior to curing.

2. Description of the Prior Art It has been thought for many years thatif excess water and air could somehow be removed from freshly mixedcementitious material (concrete or plaster) prior to curing, theresulting product would be void-free and be much stronger than thatobtained by preparation methods now used. However, the question as tohow much water is excess water and the problem of how to go aboutremoving it have not been resolved.

On the question of how much water is excess water, it is fairly welluniversally agreed that all water in excess of water of hydration isexcess water. But this has not been proven because it has beenimpossible to re- I move all water in excess of water of hydrationutilizing prior art methods and apparatus.

Many methods and types of apparatus have been used in attempts to removeexcess water from freshly mixed cementitious material. One popularmethod has been that of curing the material in a sand mold. The sandmold is supposed to absorb excess water as the material cures. Thismethod has not been successful because the sand mold only absorbs waterfrom the surface regions of the material and a non-uniform final productwhich is relatively void-free near its surface but not in its interiorresults. Another popular method has been to place freshly mixed materialin a mold having one or more small openings in it and then vibrating themold. The vibration is supposed to settle or compact the mix and excesswater is supposed to exit via the small opening or openings. This methodhas not been successful because it causes layers or strata to be formedin the material and it does not remove all excess water.

Perhaps the best conceived method for removing excess water and air fromfreshly mixed cementitious material is that disclosed by Boyle in U. S.Pat. No. 2,047,356. Boyle describes a mold in which cementitious mix canbe put under pressure to remove excess water. The mold contains aplurality of holes through which excess water and air can exit as thematerial is placed under pressureJ-Iowever, the perssure contemplated byBoyle can not possibly approach the magnitude nexessary for the removalof all excess water because the filter system (system utilized to retainthe mix in the mold while allowing excess water and air to escape)consists of .screen and canvas covering the holes through which thewater and air escapes. Boyle does not specify any particular pressure orrange of pressures, choosing rather to describe his pressure as a veryhigh pressure." At pressures up to 100 psi, or perhaps several hundredpsi, a screen and canvas filter system would be adequate. But at trulyhigh pressures, i.e., pressures up to several thousand psi, canvas,screen, water, air and mix would all be simultaneously forced outthrough the holes in the Boyle mold. Furthermore, as Boyle describes it,the process contemplated also involves vibrating the mold which, forreasons stated above, is undesirable.

SUMMARY OF THE INVENTION A filter system which enables a mold to containcementitious material while excess water and air are being expelledtherefrom under high pressure has now been found. Individual filterswhich cover openings in the mold and allow water and air to escape whilecontaining the cementitious material consist of a grooved pusher plateand a filter pad of end grain redwood board. The plate is sized andgrooved in a manner which permits water (and air) to flow around it andout through the opening which it covers. The end grain redwood boardpermits water and air but not cement to pass through it from theinterior of the mold and reach the grooves on the face of the platethrough which it can escape.

The method of this invention involves the compaction of a cementitiousmix under certain preferred high pressures for certain optimum lengthsof time. The preferred pressures and times are specified below.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of a moldsuitable for use in practicing this invention.

FIG. 2 is a cross-sectional view of the mold of FIG.

FIG. 3 is a perspective view of a pusher plate suitable for use inplacing cementitious material under pressure according to thisinvention.

FIG. 4 is a cross-sectional view of an end grain redwood board.

DESCRIPTION OF THE PREFERRED EMBODIMENT Going first to the drawing whichdepicts apparatus used in practicing this invention, FIG. 1 is anelevational view of a mold comprised of two halves 11 and 11' which maybe fastened together by means of bolts 12 or some other suitable means.A plunger 13 is shown protruding from the top of the mold. The plungeris a loose fit, allowing fluids to escape through the annulus betweenthe plunger and the mold. The plunger is for use in applying pressure tofreshly mixed cementitious material within the mold by means of apressor its equivalent. I

FIG. 2 is a cross-sectional view of the mold of FIG. 1 showing one halfof the mold ll, bolts 12, the plunger 13, and a plurality of pusherplates 14. This view depicts a plurality of openings 15, in addition tothe one through which the plunger moves, through which water and air mayescape as pressure is applied to a freshly prepared mixture ofcementitious material 16 within the mold. Depressions 17 which arelarger in diameter than openings 15 are machined into the interior wallof the mold in locations such thatthe openings lead into them. Groovedpusher plates 14 are fitted loosely into the depressions in a mannerwhereby the plates cover the openings. End grain redwood boards 18 areabutted against the interior faces of each of the plates. The boards fittightly into depressions l7, i.e., the boards have diametersapproximately equal to those of the depressions.

In order to provide annular space through which fluid may flow aroundthe grooved plates, the plates are slightly smaller in diameter than thedepressions. l-Iowever, in order to prevent the boards from beingextruded when pressure is applied to material within the mold, theannular area around the pusher plates can not be very large. The widthof the annulus should preferably not be greater than about 0.010 inch.In other words, the diameter of a pusher plate should not be less thanabout 0.020 inch smaller than that of a depression into which the platefits. In most cases an annular width of about 0.005 inch will permitsufficient fluid to pass around the periphery of a pusher plate.

FIG. 3 is a perspective view of a pusher plate 14 showing a plurality offacial grooves 19 criss-crossing its faces. Both faces are grooved inorder to permit fluid to collect on the inner face, pass through theannulus, collect on the outer face, and, finally, escape throughopenings 15 (FIG. 2). Only plates for use in conjunction with openingswhich are smaller in diameter than they are, i.e., side openings, needbe grooved on both faces.

FIG. 4 is a cross-sectional or end view of an end grain redwood board.It will be noted that the particular board depicted appears to have beencut from the exact center of a redwood leg because rings appear to becomplete. Notwithstanding FIG. 4, any end grain redwood board, whetherit be from the exact center of a log or elsewhere will suffice for thepurposes of this invention.

In operation, when pressure is applied to the mixture of cementitiousmaterial by means of a press or its equivalent pressing on the plunger,excess water and air is forced out of the cementitious material throughthe grains in the redwood boards. After passing through the boards thewater collects in the grooves on the interior faces of the pusher platesfrom whence it travels to the peripheral annulus. From the peripheralannulus of the upper pusher plate and plunger, the water escapes to theexterior of the mold. In the side ports, the water travels to thegrooves on the external faces and then out through the openings in themold.

In the foregoing description, boards 18 have been referred to as redwoodboards. While it may not be positively stated that no other wood willsufiice, certain other woods have been tried with very poor results.Balsa wood is too soft and fails when it is pressed against the groovedfaces of the plates. Water will not flow through Douglas Fir at a fastenough rate. Nor will water flow through end grain hardwood boards at afast enough rate. In order to retain cementitious material and allowwater and air to pass through, high shear strength and clean, straightgrains have been found to be necessary properties for the wood. Of woodnot tried, cedar offers a likely possibility.

By utilizing the above-described apparatus, it is possible to placefreshly prepared cementitious material under almost any high pressuredesired. The preferred method according to this invention involvesplacing freshly mixed concrete under a pressure in the range of fromabout 7,000 psi to about 15,000 psi for a length of time in the range offrom about 0.25 hour to about 6 hours and then lowering the pressure toatmospheric pressure and allowing the cencrete to cure. For plaster typematerials such as Alcast (a mixture of aluminum and Plaster of Paris)somewhat lower pressures on the order of from about 2,500 psi to about3,000 psi are preferred. Any manner presently used in the industry,i.e., fog, steam, or ambient, may be used to cure the cementitious orplaster type materials.

The following examples depict the strengths obtained from varioussamples after carrying out the above steps.

Example 1 I. Cement/sand ratio 0.510

Molding pressure 7,000 psi Molding time 6 hours Breaking strength ofproduct 13,350 psi 11. Cement/sand ratio 1.500

49152. W Molding pressure 9,040 psi Molding time 0.25 hour Breakingstrength of product 16,200 psi Sample b Molding pressure 9,040 psiMolding time 3 hours Breaking strength of product 19,700 psi Sample 0 YMolding pressure 9,040 psi Molding time 6 hours Breaking strength ofproduct 21,250 psi Example 2 1. Sample a Plaster of Paris/water ratio1.82 Molding pressure 2,820 psi Molding time 36 minutes Length of sample4,250 inches Breaking strength of product 7,800 psi Sample b Plaster ofParis/water ratio 1.82

Molding pressure 2,820 psi Molding time 36 minutes Length of sample2.125 inches Breaking strength of product 7,720 psi Sample c Alcast(50/50) wet mix Molding pressure 3,000 psi Molding time 36 minutesLength of sample 1.9 inches Breaking strength of product 4,917 psi InFIG. 2 of the drawing, it will be noted that three static filters(filters not driven by a plunger) and one active filter (filter drivenby a plunger) are depicted. These numbers may be varied. For example, ifvery short blocks of cementitious material are being prepared, oneplunger and active filter and one static filter at the bottom of themold may suffice. On the other hand, if longer blocks of cementitiousmaterial are being prepared, i.e., blocks having final lengths of about8 inches or more, it is desirable to use at least three static filtersand one plunger driven active filter. And it may be desirable to alterthe apparatus by replacing all of the static filters by plunger drivenactive filters in order that a make up volume of cement be provided tocompensate for the lost fluid and gas volumes. If very long blocks ofcementitious material, i.e., several feet long, are being prepared itmay be desirable to use a combination of six or eight or more plungersand large diameter active filters.

We claim:

1. Apparatus for removing excess water and air from freshly mixedcementitious material, said apparatus comprising:

a mold having a plurality of openings through which water and air canescape;

6 a plate covering the interior of each said opening, face of each saidplate; and

sald Plate bemg grooved and so that water means for applying pressure tocementitious material and air from the interior of said mold can reachsaid opening around it; an end grain redwood board covering the interior5 within said mold.

1. Apparatus for removing excess water and air from freshly mixedcementitious material, said apparatus comprising: a mold having aplurality of openings through which water and air can escape; a platecovering the interior of each said opening, said plate being grooved andsized so that water and air from the interior of said mold can reachsaid opening around it; an end grain redwood board covering the interiorface of each said plate; and means for applying pressure to cementitiousmaterial within said mold.